METHOD AND APPARATUS FOR MANUFACTURING HOLLOW OBJECTS, IN PARTICULAR PLASTIC PREFORMS

Abstract: Method and apparatus for manufacturing plastic objects, in particular preforms. The raw material is injected in a mould which is subsequently cooled for hardening the injected raw material into a desired object, which can be removed by means of two gripping devices (41, 42).

Description: Method and apparatus for manufacturing hollo- αhHaota . La PM SH Γ plwrtta gnfoπw This Invention relate* to a method fox manufac¬ turing hollow objects, in particular plastic preforms for subsequently prooessing to PUT objects. In a known production process PET granules are predriβd and subsequently processed in the injection moulding process to semi-finished products inch as preforms. In this case the injection .moulding process comprises a aeries of successive operations, namely metering and injecting the raw materials into a mould, subsequent pressing thereof by steaπs of a mould, and cooling and αnmoulding. In the case of preforms it is customary to remove the products from the mould by means of one gripper element provided with sleeves whieh are directly or indirectly cooled. The gripper element is provided in order to simplify the ejection proαeβs in which the preform is unmouldβd. Subsequent cooling is neoessary in this case, in order to minimise the defoxna- tion of or damage to the preforms * This can also be applied to other production of plastics. Curing the injection phase into the mould the liquid raw material is injected into the mould between its mandrel and oavity. The mandrel and the cavity are cooled during the i jeo- tion moulding process. In order to give the preforms to be unmoulded sufficient stability / the cooling ti_me must be accurately set. The cooling time is therefore an important parameter in the injection moulding oyele. The cooling time will in fact influence the total cycle time of the process. The longer the cooling time, the longer the cycle time will be, and there will thus be a reduced output. One gripper element means that there can be cool¬ ing for virtually one cycle time. However, this is still too little to reduce the cooling time during the injec¬ tion moulding process, and production continues with cycle times which are too long. In a known method, one gripper element which is provided with different sleeves as accommodation elements is used. The preforms remain two or more cycles in the sleeves on said one gripper element* The disadvantage in this case is that the gripper element is very heavy, so that more water has to be used, with a resulting increas¬ ing so-called shot weight or impulse, and with an increasing number of sleeves. This results in loss of time and a length adjustment and precision problem for the gripper, for the latter has to assume a number of dif erent positions in the mould in each case during the takeover * Early wear also occurs/ and the un oulding time increases, through the heavy handling due to the higher inertia of the apparatus. In addition, the gripper element emerges from the machine laterally, with the result that a considerable surface area is taken up and rendered useless, so that rather a large amount of space is required for the apparatus. Access to the mould is consequently made very difficult, owing to the lateral removal of the gripper element r and this is quite inooo- venient for maintenance. The use of one gripper element with sleeves, in the oaaβ of which after a cyole the preforms are dis¬ charged and deposited an an air-cooled conveyor belt with pins is also known * A first disadvantage in this ease is that cooling after one unxαoulding time cyσle is not sufficiently intensive. A further disadvantage of this method is that the positioning of the mandrels increases the complexity of the production process. in another known method, use is made of a gripper element with sleeves, in the caβe of which the preforms are cooled and conveyed to an external cooling station, which is external to the actual apparatus for carrying our the method. In addition to inadequate cooling, there is the disadvantage here of the greater complexity of the cooling stations, for, the cooling moulds generally no longer correspond to the shrinkage of the preforms during cooling * This leads to uneven cooling of the preforms and to possible damage of the preforms * For, it has bean found that preforms, in particular PBT preforms, have the best cooling properties on the outside wall (heat **-"*rp*ιmd* outwards) , and the greatest sur ace area for dissipating heat is precisely the external surface. For this reason, the use of cooled sleeves is particularly appropriate * There is therefore a great advantage when producing the preforms to allow them to cool as long as possible in the sleeves and to keep the cooling during the injection moulding phase as short as possible. The object of the invention is to eliminate the abovemβntioned disadvantages, and thus to minimiare the cooling time in the injection moulding process and transfer it externally, and to keep the preforms further in cooled sleeves. In the method for manufacturing hollow objects, in particular plastic preforms intended for subsequent proeeaeing to PBT objects, the raw material for manufac¬ turing said preforms is injected into a mould whioh has a cavity aide and a corresponding mandrel side, between wbiαh sides the preforms are formed, the mould is opened into its cavity side and mandrel side, in which ease eaoh of the mandrels of the mandrel side bears a prefoca, and a gripper element on whieh a set of aαocαnodation elements is disposed is set in motion, being driven by a drive unit for that purpose in a preset direction of movement between a deflected, disconnected position, in which said gripper element is not active and is standing ready for further movement to a working position, and said working position, which is directed at the mandrel aide of the mould/ while the pre orms are aecomαtodated in the gripper element by means of suction means, each preform being accommodated in a corresponding aααααeoda- tion element. According to the invention, at least one second gripper element is selected, and said at least one sseood gripper element is moved, by being driven by a second drive unit, between the disconnected position and the working position directed at the mandrel side of the mould, said gripper elements being synchronised with each other, for the purpose of taking over the formed preforms in succession and discharging them. This means that, thanks to the invention, the cooling carried out in the injection moulding process can be applied externally * tfn oulding will be affected with a shorter cycle time, or & shorter cooling time, and cooling will be outside the apparatus according to the invention in a cooled gripper element. This means that the preform can be cooled externally, with the result that the quality is raised. Furthermore, smaller number of sleeves is required per gripper element, with the reβult that each gripper element is considerably lighter and easier to handle, According to a further embodiment of the method according to the invention, the gripper elements are moved in a to and f o movement in the direction of their respective longitudinal axes, the gripper elements being disposed above the mould, and their respective movements relative to each other being shifted in time. This means that each gripper element can be moved vertically, i.e. in its suspension direction, with the reβult that forces associated with the movement are considerably smaller * The moment of inertia of the gripper elements is also considerably lower, and they can consequently be moved much more quickly. According to yet a further embodiment of the invention, said at leaβt two gripper elements are dis¬ posed on a carrier in an erection plane which is virtual- ly perpendicular relative to the ground, and are moved in said erection plane in a second direction, by being driven by a further drive unit between a waiting position and said disconnected working position. According to a special embodiment of the inven- tion, said at least two gripper elements are moved successively in two directions which are virtually orthogonal relative to each other, said first direction of movement being βeleoted so that it is virtually vertical relative to the ground, and the two gripper elements being moved oetween a high and a low working position respectively. According to a more specific embodiment of the invention, a first cooling time is set for cooling the injected preforms in the cavity side, while at the end of the set first cooling time the cavity side and the mandrel side of the mould are separated from each other, to a distance between them which is sufficient for the insertion of one of said gripper elements into a space thus formed between cavity side and mandrel side, the accommodation side of said one gripper element is directed towards the mandrel side, said one gripper element is moved from said disconnected high position to said space, and said one gripper element is thus taken into said low working position relative to the mandrel side, and the preforms are cooled there in the in each case corresponding accommodation elements during a second set cooling time, at the end of said cooling time the preforms are passed from the mandrel side to said one gripper element and each into an accommodation element corresponding to each mandrel, following which said one gripper element is moved back into the disconnected, high position, both gripper elements are moved crosswise until the further gripper element is in the disconnected, high position and the one gripper element is in said waiting position, and the movement carried out by said one gripper element during the completed cycle is then carried out in the same way by the further gripper element, and a further set of preforms is thus taken over by the latter from the mandrel side of the mould, and said further gripper element is then driven baok to the high position. This invention also relates to an apparatus for manufacturing hollow objects, in particular plastic preforms intended for subsequently processing to PUT objects, comprising a mould for forming said preforms, which iouid has a cavity side and a mandrel side, which sides can be taken apart, and on which mandrel sides a number of projecting mandrels are disposed, for the purpose of holding the preforms, and comprising a gripper element provided with a set of accommodation elements which can be directed at said mandrels, for cooling and receiving the preforms, said gripper element being movable, by being driven by a drive unit, between a disconnected position and a connected working position in which said gripper element is connected to the mandrel side * According to the invention, at least one second gripper alemant is provided, said gripper element being equipped with a further set of accommodation elements, by means of which the mandrels of the mandrel side of the mould can be directed, said at least second grippe . element being movable, by being driven by a further drive unit, between said disconnected position and said working position, and the latter mentioned gripper element being connected to the mandrel side, while the latter movement can be synchronized with that of the first gripper •lament. Further speαial features and advantages of the invention will emerge rom the more detailed description of an exemplary embodiment which follows with reference to appended drawings. Figure 1 is a diagrammatiα side iew of an appar- atus according to the invention. Figure 2 is a diagrammatic top view of an appar- atus according to the invention * Figure 3 is a detailed view of a part of the apparatus according to the invention. Figures 4 and 5 show further details of the view of Figure 3. Figure 6 is a partial view of a section of a mould in whieh a preform according to the invention is produced. Figures 7 to 10 are diagraam&tiα views of an apparatus according to the invention, in various posi¬ tions. An apparatus according to the invention which comprises an unmcu ding plate with two or more gripper elements is shown zn Figures 1 and 2, and in more detail in Fig. 3. Bach gripper element 41, 42, hereinafter also called gripper arm, is equipped with a set of sleeves IS, one sleeve being provided for each mandrel 31 of a mould 30 which has a mandrel side 33 and a cavity side 32. The number of sleeves in the gripper arm 41, 42 is determined by the number of mandrels 31 in the mould. The production method consists of injection moulding so-called preforms 50 by means of an injection moulding machine 35 having an inbuilt injection mould. At the end of a first cycle time the machine is opened and the mould 30 splits into a cavity side 32, or the hollow side, on the one hand / and a mandrel side 33, on the other. The cavity side 32 of the mould 30 is situated on a fixed machine platform 36, while the mandrel side 33 is fixed on a movable platform 37 of the machine. When said cycle has ended, the hollow products SO remain on the respective mandrels 33 of the mandrel side, due to the retaining action of a so-called mandrel puller 38 by way of a locally fitted clamping connection, for example a threaded connection 39, such as that shown in Figure 6. The mandrel puller comprises, for example, two ring halves whioh ace connected to each other around the base of each mandrel 31. During the ejection of the preforms the mandrel puller is pushed a certain distance along the mandrel wall towards the tip of the mandrel, in the course of which, due to said threaded connection 39 between mandrel puller B and preform 50, the base of the preform 50 is pulled along the mandrel 3 , and the preform is thus prepared for its takeover by the gripper element 41, 42. During opening of the machine the mandrel side opens with the movable platform 37, and an opening is produced between the cavity side and the mandrel side. Said space 34 is produced in order to give access for one of the gripper arms 41, 42 between the cavity side and the mandrel side of the mould. One gripper arm, for example 41, is positioned from a high, disconnected position B (Figure 7} until it is between the mould, in - ■ which case during e ectio the preforms 50 can be trans¬ ferred easily to the sleeves 16 of one gripper arm 41, into the working position C (Fig. 8) . The gripper arm can be set in motion by, for example, a hydraulic, electric or pneumatic drive motor 21. The sleeves on the gripper arm are positioned in a way corresponding to the cαrres-** ponding mandrels on tbβ mould. On reaching working position C, in which the ends of the sleeves 16 are a short distance from the corrββ- ponding mandrel tips, the preforms 50, which are already partially ejected from the mandrel 31, are βuoked into the respective sleeves 16 by the action of euitαbl* suction means 60, for example a suction pump. When the preforms 50 have been transferred from mandrel to sleeve, the one gripper arm 41 returns to the disconnected position which iβ shown by B in Figure . The preforms can be transferred in various ways, for example through vacuum suction by the sleeves or by ejection of the preforms from the mandrel, or also by both, ejection and then suction. According to the invention, a so-called multiaxiβ gripper arm device is provided, which gripper arm com¬ prises at least a second gripper element 42, the two gripper elements 41, 42 each being driven individually by means of a separate drive unit 21, 22 designed for ths purpose. The interaction of the two gripper arms , 42, which according to the invention are synchronized, is described below with reference to Figures 7 to 10. Duriag said first cycle SI the machine opens at the end of a i st cooling period (first cooling) , in which ease injected preforms 50 are resting on the mandrel side of the mould, as shown in Figure 6 . As soon as a space 34 is formed between mandrel side 33 and cavity side 32 which is large enough to place the first gripper arm 41 between mandrel side and cavity side, and a reliable transfer of the preforms iβ possible, the gripper arm 41 is moved, by being driven by the motor 21, along 71 axis between the mandrel side and cavity side of the mould, as shown in Figure B, until it is in the transfer position, which is the working position shown by C. The first gripper element 41 then takes over a complete first set of preforms 81 from the mandrel side 33 of the mould. When the preforms have been transferred, the first gripper arm 41 with Yl axis is driven back to the disconnected or high position (see Fig. 7). In that position the preforms 50 are held in the respective 3leeves 16 of the first gripper arm 41 during a subsequent cycle SV1 which starts frost the moment that the first gripper element 41 is driven into said disconnected position £. Here the preforms 50 are accommodated in their respective sleeves- where they are subjected to an appropriate cooling. Shortly before the end of cycle SV1 ths second gripper arm 42 is moved from the waiting position A into the disconnected, high position B, while the first gripper arm 41 is moved to the non-active waiting posi¬ tion shown by ' in Figure 9. This movement of the two gripper elements 41 and 42 is preferably simultaneous in the direction of arrow X, where carrier plate 10 is moved by being driven by a further motor 11 (see Figure 9), but this movement can be achieved in any other way. A similar takeover process is carried out with the βeσond gripper element 42. During cycle svi the machine opens at the end of ths cooling time, and injected preforms are resting on the mandrel side * When a space is formed between mandrel side and cavity side of the mould which is large enough to move ths second gripper arm 42 into said space in working position C, and a reliable transfer of ths pre¬ forms is made possible, the second gripper arm 42, which is driven by a second motor 22, passes between the two mould sides, into transfer position C, as can be seen in Figure 10. Here, gripper arm 42 takes over a complete further set of preforms S2 from the mould, when the transfer has been completed, the second gripper element 42 is transferred in the 32 direction to the disconnected position, where the preforms are held in corresponding sleeves 16 of the gripper element 42 during a subsequent cycle SV2, which starts when the gripper element 42 is driven into the disconnected position B. In the meantime, the preforms of cyole SI are still present in the second gripper arm 42. Shortly before the end of the cycle SV2, the first gripper arm 41 is moved into the disconnected position B, and thereby also the second gripper arm 42 into the non-active waiting position shown by A' in Figure 10. After the first gripper arm 41 Λt. reached the disconnected poβi- tion, its preforms 50 are removed by known means. During cycle SV2 the machine opens at the end of the cooling period and injected preforms are resting on the mandrels of the mandrel side. When a space 34 is formed between mandrel side and cavity side of the mould hich is large enough to receive the gripper arm, and a reliable trans¬ fer of the preforms is possible, gripper arm 41, being driven by motor 21, passes between the mandrel side and cavity side of the mould, into working position C, and takes over a complete set of preforms SV2 from the mould. When the transfer has been completed, the first gripper arm 41 is driven in the Yl movement to the disconnected position B« In that position the preforms are held in the corresponding sleeves of the first gripper arm 41 during a subsequent cyeie SV3, which startπ when the first gripper element 41 goes into the disconnected position * In the meantime, the preforms SV2 are still present in the second gripper arm 42. Shortly before ths ending of the cycle SV3, the second gripper arm 42 moves into the discαnneoted position B, and first gripper arm 41 is also moved into non-active waiting position A. After ths second gripper arm 42 has reached the disconnected position, its preforms are removed by known means. During cycle £V3 the machine opens at the end of the cooling period. Injected preforate are than resting on the mandrel side of the mould. When a space has formed between mandrel side and cavity aide which is large enough to place the gripper arm between them, and a reliable transfer of the preforms is possible, gripper ana 42, driven by second motor 22, passes between the respective mould siάeu into transfer position c f and takes over a complete set of preforms SV3 from the mould. When the transfer has been completed, the second gripper arm 42, driven by motor 22, passes in Y2 movement to the disconnected position. In that position the preforms are heid in the second gripper arm 42 during the next cyole SVn, which βtart3 when ths gripper arm 42 goes into the disconnected outboard position B. in the meantime, the preforms SV2 are still present in the gripper arm. Shortly before the ending of the cycle SVn, the first gripper arm 41 is driven into the disconnected position B, and the second gripper arm 42 is also moved into non- active waiting position A. After the first gripper arm 41 has reached the disconnected position, the preforms of said first gripper arm 41 are removed by known means. The a ovementioned steps are repeated for the next cycle, in a repeated process. It should be understood that in cycle SI the two gripper arms 41 and 42 are regarded as being empty, so that their mutual interaction can be explained better. Thanks to this invention the preforms remain longer in the cooled sleeves, i.e. two cycle times - minus the time for the release of ths preforms - up in the disconnected position, until the following cycle * Ths preforms are also of better quality, for they are less damaged and less bent. This in addition leads to a better subsequen processing of the PET preform in a blow moulding machine, where each preform is given its final form by blow moulding it, for example to a PBT bottle. A shortened cycle time is also obtained. The internal cooling time of an injection moulding process is partially transferred to the external cooling of the gripper arm, with the result that the injection moulding process can be π-aintained undisturbed (and not inter¬ rupted by an internal cooling cycle) . Furthermore, the accessibility of the mould is considerably improved. Due to the fact that the method is carried out in the vertical direction, less βpaββ is required, since everything is carried out in the vertical direction, such as said Y movement of the gripper arms. Consequently, the front and rear sides of the mould are easily accessible. This is particularly beneficial in the case of repairs or when changing the type of preform to be manufactured. It should also be pointed out that the above- described invention can be used for all hollow plastic products. Thanks to the vertical Y movement, it is also possible to dispense with heavy frames for the gripper arms, which has a beneficial effect on their handling. If necessary, two bearing plates or bearing tables 10 can be used, namely each with one gripper arm (separate con- trol).

Claims: l. Method for manufacturing hollow objects, in particular plastic preforms for subsequently processing to PET objects, in which the raw material far menufac- turing said preforms (50) is injected into a mould (30) whicn has a cavity side (32) and a corresponding mandrel side (33), between which sides the preforms (50) are formed, the mould is opened into its cavity Bid* and mandrel side, in which case each of the mandrels (31) of the mandrel side bears a preform, and a gripper element (41) on which a set of accommodation elements (16) is disposed is set in motion, being driven by a drive unit (21) for that purpose in a, preset direction of movement between a deflected, disconnected position (B), in which said gripper element (41) is not active and is standing ready for further movement to a working position (C), and βaid working position (C), which is directed at the mandrel side of the mould, while the preforms (50) are accommodated in the gripper element (41) by means of suction means (60), each preform being accommodated in a corresponding accommodation element (16), characterized in that at least one second gripper element (42) is selected, and said at least one second gripper element (42) is moved, by being driven by a second drive unit (22., between the disconnected position (B) and the working position (C) directed at the mandrel aide (33) of the mould (30), said gripper elements (41, 42) being syn¬ chronized with eaoh other, for the purpose of taking over the formed preforms in succession and discharging them. 2. Method according to Claim 1, characterised it that the gripper elements (41, 42) are moved in a to and fro movement in the direction of their respective longi¬ tudinal axes (Yl. Y2) , the gripper elements [41, 42) being disposed above the mould (3C) , and their respective movements relative to eaoh other being shifted in time. 3. Method according to one of the preαeding claims, characterized in that said at least two gripper elements (41, 42) are disposed on a carrier (1C) in an erection plane which is virtually perpendicular relative to the ground and are moved in said erection plane in a second direction, by being driven by a further drive unit (11) between a waiting position (A) and βaid disconnected working position (B). 4. Kβthod according to the preceding claim, charac¬ terized in that said at least two gripper elements are moved successively in two directions which are virtually orthogonal relative to each other, said first direction of movement being selected so that it is virtually vertical relative to the ground, and the two gripper elements beinq moved between a high and a low working position (B and C respectively). 5. Method according to the preceding claim chαrac- tβrized in that a first cooling time is set for oooling the injected preforms (50) in the cavity side (32), in that at the end of the set first cooling time the cavity side (32) and the mandrel side (33) of the mould (30) ere separated from each other, to a distance between them which is sufficient for the insertion of one of said gripper elements (41, 42} into a space (34) thus formed between cavity side and mandrel side, the accommodation side (44) of said one gripper element is directsd towards the mandrel side (33), said one gripper element is moved from said high position (B) to said space (34), and said one gripper element is thus taken into said low working position (C) relative to the mandrel side, and the preforms (50) are cooled there in the in each case corresponding accommodation elements during a second set cooling time, at the end of said cooling time the pre¬ forms are passed rom the mandrel side to said one grip¬ per element and each into an accommodation element (16) corresponding to each mandrel (33), following which said one gripper element is moved back into the disconnected, high position (B) , both gripper elements are moved cross¬ wise until the further gripper element is in the discon¬ nected, high position (B) and the one gripper element in said waiting position (A), and the movement carried out by said one gripper element during the completed cycle is then carried out in the same way by the further gripper element, and a further set of preforms (50) is thus taken over by the latter from the mandrel side of the mould (30), and said further gripper element is then driven back to the high position (B) . 6. Apparatus for manufacturing hollow objects, in particular plastic preforms intended for subsequently processing to PET objects, comprising a mould (30) for forming said preforms (50), which mould has a cavity side (32) and a mandrel side (33), which sides can be taken apart, and on which mandrel sides a number of projecting mandrels (31) are disposed, for the purpose of holding the preforms, and comprising a gripper element (41) provided with a. set of accommodation elements (16) which can be directed at said mandrels (31), for cooling and receiving the preforms, said gripper element being movable, by being driven by a drive unit (21), between a disconnected position (B) and a connected working posi¬ tion (C) in which said gripper element is connected to the mandrel side (33), characterized in that at least one second gripper element (42) is provided, which second element is equipped with a further set of accommodation elements (16) by means of which the mandrala (31) of the mandrel side of the mould (30) can be directed, hile said at least second gripper element (42), being driven by a further drive unit (22), can be moved between said disconnected position (S) and said working position (C) , and the latter gripper element (42) iβ connected to the mandrel side (33) , while the latter movement can be synchronized with that of the first gripper element (41).

Inventors: CUYPER DIRK DE, DE CUYPER, DIRK
Applicants: CUYPER DIRK DE, SERVIPLAST, DE CUYPER, DIRK
Application year: 1994
Main classification: B29C45
IPC codes: B29C33, B29C45, B29C49